2,432 research outputs found
Cloud Chamber Investigation of Anomalous θ^0 Particles
Eighteen anomalous θ^0, (θ^0_(anom)), decay events observed in the California Institute of Technology magnet cloud chambers have been analyzed. Many of these decays are dynamically inconsistent with the τ^0→π^++π^−+π^0 scheme, but most are consistent with the decay processes: θ^0_(anom)→π^++π^−+γ, π^±+μ^∓+ν, and π^±+e^∓+ν. However, at least one event is inconsistent with each decay scheme. From the locations of the decays in the cloud chamber, the lifetime is found to be significantly longer than that of the normal θ^0 particle, called here the θ^0_(π2) particle. Other differences in the behavior of the θ0anom and θ^0_(π2) particles were also observed in the (a) momentum distributions, (b) origin locations, (c) relative numbers of θ^0_(anom) and θ^0_(π2) particles traveling upward, and (d) the types of V particles produced in association with the θ^0_(anom) and θ^0_(π2). It is concluded that not all the θ^0_(anom) decays can result from alternate decay modes of the θ^0_(π2). Moreover, many decays can be neither τ^0 decays nor alternate decays of the θ^0_(π2).
The characteristics of the θ^0_2 particle proposed by Gell-Mann and Pais are consistent with those of the θ^0_(anom) particle, with the possible exception of the observed types of associations. An estimate was made of the relative number of θ^0_(anom) to θ^0_(π2) particles observed to decay in the cloud chamber. If all θ^0_(anom) decays are assumed to arise from decays of the θ^0_2 particle, then a lower limit for the θ^0_2 lifetime is found to be about 10^(−9) sec
Soft-core hyperon-nucleon potentials
A new Nijmegen soft-core OBE potential model is presented for the low-energy
YN interactions. Besides the results for the fit to the scattering data, which
largely defines the model, we also present some applications to hypernuclear
systems using the G-matrix method. An important innovation with respect to the
original soft-core potential is the assignment of the cut-off masses for the
baryon-baryon-meson (BBM) vertices in accordance with broken SU(3), which
serves to connect the NN and the YN channels. As a novel feature, we allow for
medium strong breaking of the coupling constants, using the model with
a Gell-Mann--Okubo hypercharge breaking for the BBM coupling. We present six
hyperon-nucleon potentials which describe the available YN cross section data
equally well, but which exhibit some differences on a more detailed level. The
differences are constructed such that the models encompass a range of
scattering lengths in the and channels. For the
scalar-meson mixing angle we obtained values to 40 degrees, which
points to almost ideal mixing angles for the scalar states. The
G-matrix results indicate that the remarkably different spin-spin terms of the
six potentials appear specifically in the energy spectra of
hypernuclei.Comment: 37 pages, 4 figure
A high resolution wire scanner for micron-size profile measurements at the SLC
Fine conductive fibers have been used to measure transverse beam dimensions of a few microns at the Stanford Linear Collider (SLC). The beam profile is obtained by scanning a fiber across the beam in steps as small as 1 [mu]m, and recording the secondary emission signal at each step, using a charge sensitive amplifier. We first outline the mechanical construction and the analogue electronics of the wire scanner. We then describe its performance in test beams and in actual operation. The article closes with a brief discussion of performance limitations of such a beam profile monitor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28112/1/0000561.pd
The hyperon-nucleon interaction: conventional versus effective field theory approach
Hyperon-nucleon interactions are presented that are derived either in the
conventional meson-exchange picture or within leading order chiral effective
field theory. The chiral potential consists of one-pseudoscalar-meson exchanges
and non-derivative four-baryon contact terms. With regard to meson-exchange
hyperon-nucleon models we focus on the new potential of the Juelich group,
whose most salient feature is that the contributions in the scalar--isoscalar
(\sigma) and vector--isovector (\rho) exchange channels are constrained by a
microscopic model of correlated \pi\pi and KKbar exchange.Comment: 28 pages, 8 figures, submitted to Lecture Notes in Physic
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GEM-type detectors using LIGA and etchable glass technologies
Gas electron multipliers (GEMS) have been made by a deep X-ray lithography technique (LIGA process) using synchrotron radiation on polymethylmethacrylate (PMMA) and by UV processes using a UV etchable glass. Gain, stability and rate capability for these detectors are described.The LIGA detectors described consist of PMMA sheets of various thicknesses, 125mm to 350mm, and have 150mm x 150mm square holes spaced with a pitch of 300mm. Thin copper electrodes are plated on the top and bottom surfaces using a Damascene method, followed by electroless plating of the copper onto a palladium-tin base layer. For various thicknesses of PMMA measurements have been made of absolute gain vs. voltage, time stability of gain, and rate capability. The operating gas mixture was usually Ar/CO2 (70/30) gas, but some tests were also done using P10 gas. We also made GEM-like detectors using the UV etchable glass called Foturan, patterned by exposure to UV light and subsequent etching. A few measurements using these detectors will be reported, including avalanche gain and time stability
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions
The weak nucleon axial-vector form factor for quasi-elastic interactions is
determined using neutrino interaction data from the K2K Scintillating Fiber
detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of
which half are charged-current quasi-elastic interactions nu-mu n to mu- p
occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for
oxygen and assume the form factor is approximately a dipole with one parameter,
the axial vector mass M_A, and fit to the shape of the distribution of the
square of the momentum transfer from the nucleon to the nucleus. Our best fit
result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated
vector form factors from recent electron scattering experiments and a
discussion of the effects of the nucleon momentum on the shape of the fitted
distributions.Comment: 14 pages, 10 figures, 6 table
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